Reinforcing overlay for matrix bit bodies

ABSTRACT

A drill bit that includes a matrix bit body having a reinforcing overlay thereon and having at least one blade thereon; at least one cutter pocket disposed on the at least one blade; at least one cutter disposed in the at least one cutter pocket; and a braze material disposed between the at least one cutter and the at least one cutter pocket, wherein the reinforcing overlay comprises carbide particles and at least one binder and has a melting point greater than a melting point of the braze material is disclosed.

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed herein relate generally to PDC bit bodies. Inparticular, embodiments disclosed herein relate generally to PDC matrixbit bodies having a reinforcing overlay disposed thereon.

2. Background Art

Polycrystalline diamond compact (“PDC”) cutters are known in the art foruse in earth-boring drill bits. Typically, bits using PDC cuttersinclude an integral bit body which may be made of steel or fabricatedfrom a hard matrix material such as tungsten carbide (WC). A pluralityof PDC cutters is mounted along the exterior face of the bit body inextensions of the bit body called “blades.” Each PDC cutter has aportion which typically is brazed in a recess or pocket formed in theblade on the exterior face of the bit body.

The PDC cutters are positioned along the leading edges of the bit bodyblades so that as the bit body is rotated, the PDC cutters engage anddrill the earth formation. In use, high forces may be exerted on the PDCcutters, particularly in the forward-to-rear direction. Additionally,the bit and the PDC cutters may be subjected to substantial abrasiveforces. In some instances, impact, vibration, and erosive forces havecaused drill bit failure due to loss of one or more cutters, or due tobreakage of the blades.

As mentioned above, when designing a PDC bit, the bit body may beselected from a steel bit body and a matrix bit body. While steel bodybits may have toughness and ductility properties which make themresistant to cracking and failure due to impact forces generated duringdrilling, steel is more susceptible to erosive wear caused byhigh-velocity drilling fluids and formation fluids which carry abrasiveparticles, such as sand, rock cuttings, and the like. Thus, steel bodyPDC bits are generally coated with a more erosion-resistant material,such as tungsten carbide, to improve their erosion resistance.

Typically, a hardfacing material is applied, such as by arc or gaswelding, to the exterior surface of the drill bit to protect the bitagainst erosion and abrasion, such as by techniques described U.S. Pat.No. 6,601,475, which is herein incorporated by reference in itsentirety. Hardfacing is typically applied to the bit prior to brazing ofthe cutters to the to the bit body. The hardfacing material typicallyincludes one or more metal carbides, which are bonded to the steel bodyby a metal alloy (“binder alloy”), which is typically a steel alloy. Ineffect, the carbide particles are suspended in a matrix of steel forminga layer on the surface of the steel substrate. The carbide particlesgive the hardfacing material hardness and wear resistance, while thematrix metal provides fracture toughness to the hardfacing. Some typicalmethods of application of hardfacing include various welding techniques,high velocity cold spray methods, plasma spray and other thermal spraytechniques. As improvements in hardfacing materials and applicationtechniques have been made, hardfacing materials used on steel bit bodiesgenerally exhibit better erosion and abrasion resistance than the matrixmaterial used in matrix bit bodies. Hardfacing materials have also beenapplied in localized regions of a bit body, such as, for example, in thearea surrounding the cutter pocket described in U.S. Pat. No. 6,772,849,which is herein incorporated by reference in its entirety.

In current bit design practices, over seventy five percent of PDC bitsare made from matrix bit bodies, mainly because a matrix bit body offerssuperior erosion resistance as compared to hardfaced steel bodies. Withthe advent of improved hardfacing materials, the hardfacing materialsused on steel bit bodies exhibit better erosion and abrasion resistanceas compared to the matrix material itself. However, one of the primaryissues concerning hardfacing of steel body bits is the bonding andcoverage of the hardfacing material in between pockets and the base ofthe pockets. During drilling, fluids seep under the hardfacing and erodethe steel body. In some instances, because of poor bonding and lack ofsupport, hardfacing material chips off from the surfaces exposing thesteel. Thus, difficulties in obtaining good and uniform coverage of thebit body are readily apparent and result in significant erosion of thematerial, especially in the area surrounding the cutters and cutterpockets.

Further, many hardfacing materials used are relatively hard and brittle.During use of hardfaced bits, a thin coating of the erosion-resistantmaterial may crack, peel off or wear, exposing the softer steel bodywhich is then rapidly eroded. This can lead to loss of PDC cutters asthe area around the cutter is eroded away, causing the bit to fail. Dueto the high failure rates caused by the undercutting of the steel bodyand poor coverage of hardfacing near and between the cutter pockets, atypical steel body bit generally achieve only 1-2 runs per bit.

The matrix bit body generally is formed by packing a graphite mold withtungsten carbide powder and then infiltrating the powder with a moltencopper-based alloy binder. For example, macrocrystalline tungstencarbide and cast tungsten carbide have been used to fabricate bitbodies. Macrocrystalline tungsten carbide is essentially stoichiometricWC which is, for the most part, in the form of single crystals. Somelarge crystals of macro-crystalline WC are bi-crystals. Carburizedtungsten carbide has a multi-crystalline structure, i.e., they arecomposed of WC agglomerates. Cast tungsten carbide, on the other hand,is formed by melting tungsten metal (W) and tungsten monocarbide (WC)together such that a eutectic composition of WC and W₂C, or a continuousrange of compositions therebetween, is formed. Cast tungsten carbidetypically is frozen from the molten state and comminuted to a desiredparticle size.

A third type of tungsten carbide, which has been typically used inhardfacing, is cemented tungsten carbide, also known as sinteredtungsten carbide. Sintered tungsten carbide comprises small particles oftungsten carbide (e.g., 1 to 15 microns) bonded together with cobalt.Sintered tungsten carbide is made by mixing organic wax, tungstencarbide and cobalt powders, pressing the mixed powders to form a greencompact, and “sintering” the composite at temperatures near the meltingpoint of cobalt. The resulting dense sintered carbide can then becrushed and comminuted to form particles of sintered tungsten carbidefor use in hardfacing.

Bit bodies formed from either cast or macrocrystalline tungsten carbideor other hard metal matrix materials, while more erosion resistant thansteel, lack toughness and strength, thus making them brittle and proneto cracking when subjected to impact and fatigue forces encounteredduring drilling. This can result in one or more blades breaking off thebit causing a catastrophic premature bit failure. Additionally, thebraze joints between the matrix material and the PDC cutters may crackdue to these same forces. The formation and propagation of cracks in thematrix body and/or at the braze joints may result in the loss of one ormore PDC cutters. A lost cutter may abrade against the bit, causingfurther accelerated bit damage. However, bits formed with sinteredtungsten carbide may have sufficient toughness and strength for aparticular application, but may lack other mechanical properties, suchas erosion resistance.

In designing matrix bit bodies, there is often a compromise betweenachieving good wear resistance/hardness and toughness because wearresistance/hardness and toughness tend to be inversely related. Effortsto enhance one property usually result in a trade-off of the other.Thus, it is difficult to achieve both good wear resistance (especiallyerosion resistance) in demanding applications while maintaining adequatetoughness. To provide adequate toughness for many applications, erosionof the matrix bit body will generally minimize the life of a matrix bitbody to 1-3 runs per bit by reducing the capability to rebuild the bit.Additionally, another issue surrounding the use of matrix bit bodiesinvolves cracking of the bit body that can result from the multiple heatcycles that a bit must undergo during brazing. Furthermore, hardfacingmaterials which have been conventionally applied to steel bit bodies toimprove wear/erosion resistance have never been extended to matrix bitbodies because the difference in the substrate material, i.e., matrixmaterial, has always been thought to prevent adhesion/bonding of thehardfacing materials to the matrix body substrate.

Accordingly, there exists a need for a new matrix body which has highstrength and toughness, resulting in improved ability to retain bladesand cutters, while maintaining other desired properties such as wear anderosion resistance.

SUMMARY OF INVENTION

In one aspect, embodiments disclosed herein relate to a drill bit thatincludes a matrix bit body having a reinforcing overlay thereon andhaving at least one blade thereon; at least one cutter pocket disposedon the at least one blade; at least one cutter disposed in the at leastone cutter pocket; and a braze material disposed between the at leastone cutter and the at least one cutter pocket, wherein the reinforcingoverlay comprises carbide particles and at least one binder and has amelting point greater than a melting point of the braze material.

In another aspect, embodiments disclosed herein relate to a drill bitthat includes a matrix bit body having a reinforcing overlay thereon andhaving at least one blade thereon; at least one cutter pocket disposedon the at least one blade; at least one cutter disposed in the at leastone cutter pocket; and a braze material disposed between the at leastone cutter and the at least one cutter pocket, wherein the reinforcingoverlay comprises carbide particles and at least one binder and has ahardness greater than about 50 HRc.

In yet another aspect, embodiments disclosed herein relate to a methodof forming a drill bit that includes forming a matrix bit body having atleast one blade thereon, wherein the at least one blade has at least onecutter pocket disposed thereon; applying a reinforcing overlay to theformed matrix bit body; and brazing at least one cutter in the at leastone cutter pocket with a braze material.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a PDC drill bit.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a matrix bit bodyfor a fixed cutter or PDC drill bit having a reinforcing overlaydisposed thereon. Referring to FIG. 1, a fixed cutter drill bit 10 has amatrix bit body 12 on which a reinforcing overlay may be disposed (notshown). The lower face of the bit body 12 is formed with a plurality ofblades 14, which extend generally outwardly away from a centrallongitudinal axis of rotation 16 of the drill bit. A plurality of PDCcutters 18 are disposed side by side along the length of each blade. Thenumber of PDC cutters 18 carried by each blade may vary. The PDC cutters18 are individually brazed to a stud-like carrier (or substrate), whichmay be formed from tungsten carbide, and are received and secured(brazed) within sockets in the respective blade.

Matrix Bit Bodies

As described above, a matrix bit body may include tungsten carbideparticles may be surrounded by a metallic binder. The matrix bit bodymay be formed, for example, by packing a graphite mold with tungstencarbide powder and then infiltrating the powder with a molten binder.Among the types of tungsten carbide particles used in the fabrication ofthe bit body, those generally used include, for example,macrocrystalline tungsten carbide, cast tungsten carbide, carburizedtungsten carbide, and cemented or sintered tungsten carbide.

In an infiltrated bit body, the metallic binder surrounding the tungstencarbide particles may be formed from a metallic binder powder and aninfiltration binder. The metallic binder powder may be pre-blended withthe matrix powder hard carbide particles, which is then is infiltratedby an infiltration binder. The term “infiltration binder” herein refersto a metal or an alloy used in an infiltration process to bond thevarious particles of tungsten carbide forms together. Suitable metalsinclude all transition metals, main group metals and alloys thereof. Forexample, copper, nickel, iron, and cobalt may be used as the majorconstituents in the infiltration binder. Other elements, such asaluminum, manganese, chromium, zinc, tin, silicon, silver, boron, andlead, may also be present in the infiltration binder. In one embodiment,the infiltration binder is selected from at least one of nickel, copper,and alloys thereof. In another embodiment, the infiltration binderincludes a Cu—Mn—Ni—Zn alloy. Such matrix bit bodies may have, forexample, a hardness ranging from 38-45 HRc, a fracture toughness of atleast 20 ksi(in^(0.5)), and a transverse rupture strength of at least120 ksi in one embodiment and ranging from about 130 to 180 in anotherembodiment.

In one embodiment, the matrix powder comprises a mixture of tungstencarbides and a metallic binder powder. In a particular embodiment,nickel and/or iron powder may be present as the balance of the matrixpowder, typically from about 2% to 12% by weight. In addition to nickeland/or iron, other Group VIIIB metals such as cobalt and various alloysmay also be used. For example, it is expressly within the scope of thepresent invention that Co and/or Ni is present as the balance of themixture in a range of about 2% to 15% by weight. Metal addition in therange of about 1% to about 15% may yield higher matrix strength andtoughness, as well as higher braze strength.

The matrix powder mixture may include at least 80% by weight carbide ofthe total matrix powder. While reference is made to tungsten carbide,other carbides of Group 4a, 5a, or 6a metals may be used. Although thetotal carbide may be used in an amount less than 80% by weight of thematrix powder, such matrix bodies may not possess the desired physicalproperties to yield optimal performance.

The amount of the metallic binder and carbide hard particles in formingthe matrix body may range, in one embodiment, in a ratio of from 30:70to 40:60 by volume (binder:carbide). In other embodiments, the totalcarbide may be used in an amount less than 60% by volume or greater than70% by volume of the matrix body, such matrix bodies may also notpossess the desired physical properties to yield optimal performance.

While reference has been made to forming the matrix bit bodies disclosedherein by an infiltration process, no limitation is intended by suchdescription. Rather, it is specifically within the scope of the presentinvention that a matrix bit body formed by any technique, including forexample hot pressing or casting, as described in U.S. Patent PublicationNo. 2005/0247491, which is herein incorporated by reference in itsentirety, may be used in conjunction with the reinforcing overlaysdisclosed herein.

Reinforcing Overlay

The reinforcing overlay that may be disposed on the matrix bit bodyaccording to various embodiments disclosed herein may include particlesof tungsten carbide or other wear resistant particles (e.g., borides,nitrides, carbides or mixtures thereof) bonded to the matrix bit body bya metal alloy, which is also generally referred to as a binder alloy. Ineffect, the carbide particles are suspended in a matrix of metal forminga layer on the surface. The wear resistant particles give thereinforcing overlay hardness and wear resistance, while the matrix metal(or alloy) provides fracture toughness to the reinforcing overlay andcontributes to the bonding between the reinforcing overlay and thematrix bit body.

Various types of tungsten carbide may be used in the reinforcingoverlay, including cast tungsten carbide, macro-crystalline tungstencarbide, cemented tungsten carbide, and carburized tungsten carbide. Oneof ordinary skill in the art would recognize that the types, sizes,percentages of the various carbide particles may be varied depending onthe properties desired in the reinforcing overlay for a particularapplication. In various embodiments, carbide combinations suitable foruse in the reinforcing overlay disclosed herein may include thosecombinations described in U.S. Pat. Nos. 4,836,307, 5,791,422,5,921,330, and 6,659,206, which are herein incorporated by reference intheir entirety.

In one embodiment, the carbide content in the reinforcing overlay mayvary from about 40 to 80 weight percent, with a binder alloyconstituting the balance of the reinforcing overlay. Binder alloys thatmay be used in various embodiments disclosed herein may include Ni andCo. In other embodiments, the binder alloy may include Group VIII metalssuch as Co, Ni, Fe, alloys thereof, or mixtures thereof. By applying areinforcing overlay comprised of a binder alloy, such as Ni- or Co-basedalloys, to a matrix bit body having a composition as disclosed herein,with the present inventors have advantageously discovered that thecombination of the particular binder and matrix body compositionprovides adequate adhesion/bonding of the reinforcing overlay to thematrix substrate. As shown in Table 1 below, various examples ofreinforcing overlays suitable for use in the present disclosure arelisted.

Method of Melting or Fusion Coating Composition Application Hardness(HRc) Point Deloro Stellite 50 WC/NiCrFeSiBC Spray fused/laser 49–52 M:~1063° C. cladded D-Gun 2040 WC/CoC Super D-Gun 64–69 — Colmonoy 750WC/NiWCrCoSiFeB Flame sprayed/laser 58–63 F: ~1060° C. cladded GHF5WC/CoCrNiBSi Flame sprayed/oxy- 63–70 — acetylene welded Praxair LW-1N30WC/Co D-Gun 70–72 —

Many factors affect the durability of the reinforcing overlay in aparticular application. These factors include the chemical compositionand physical structure (size, shape, and particle size distribution) ofthe carbides, the chemical composition and microstructure of the matrixmetal or alloy, and the relative proportions of the carbide materials toone another and to the matrix metal or alloy. While higher proportionsof the wear-resistant particles will increase the wear resistance of thereinforcing overlay, unfortunately it decreases the fracture toughnessof the hardfacing overlay and weakens the bonding between thereinforcing overlay and the underlying matrix body.

In one embodiment, the reinforcing overlay may have a hardness greaterthan that of the matrix bit body on which it is disposed. In otherembodiments, the reinforcing overlay has a hardness of greater thanabout 50 HRc; from about 50 to 75 HRc in another embodiment; and greaterthan about 60, 65, and 70 HRc in various other embodiments. In anotherembodiment, the reinforcing overlay may have a strength greater than thestrength of the matrix bit body on which the reinforcing overlay isdisposed.

In some embodiments, the melting point of the reinforcing overlay may beselected in accordance with a particular process of manufacturing thematrix bit body having a reinforcing overlay thereon. That is, themelting point of the reinforcing overlay may be selected to be greaterthan that of the braze material used to secure the PDC cutting elementto the matrix bit body if the reinforcing overlay is applied prior tobrazing the cutting elements to the bit body, and conversely, less thanthe melting point of braze material if the reinforcing overlay isapplied subsequent to the brazing of the cutting elements to the bitbody. In a particular embodiment, the reinforcing overlay has a meltingpoint greater than that of the braze material used to secure the PDCcutters to the matrix bit body. In another particular embodiment, thereinforcing overlay has a melting point greater than about 1000° C. Inyet another particular embodiment, the reinforcing overlay has a meltingpoint ranging from about 1050 to 1400° C.

The reinforcing overlay may be disposed on substantially all surfaces ofthe matrix bit body. The thickness of the reinforcing overlay may rangefrom about 0.01 to 0.125 inches in one embodiment. One of skill in theart would recognize the thickness need not be uniform across allsurfaces of the matrix bit body; rather, it is within the scope of thepresent invention that the thickness may be varied to optimizeperformance.

Additionally, while the described embodiments make reference to a singlereinforcing overlay, no limitation is intended on the scope of theinvention by such a description. In fact, during application of thereinforcing overlay, multiple layers of a reinforcing overlay may beapplied to the bit body. If multiple layers of a reinforcing overlay areprovided, one of ordinary skill in the art would recognize thatcompositions and resulting properties may be varied across the multiplelayers to promote bonding and adhesion of the reinforcing overlay to thematrix body substrate.

Application of Reinforcing Overlay

The reinforcing overlay disclosed herein may be applied to the matrixbit body by using one of several various spraying techniques. In variousparticular embodiments, the reinforcing overlay may be applied by one ofa d-gun, spray-and-fuse, or high velocity cold spray technique.

D-gun (detonation gun) coatings, such as, for example, those describedin U.S. Pat. No. 5,535,838, which is herein incorporated by reference inits entirety, include those coatings applied by the use of a d-gun. Thed-gun process includes gases, usually consisting of oxygen and a fuelgas mixture, that are fed into a barrel of the gun along with a chargeof fine tungsten carbide-based powder. The gases and the resultingdetonation wave heat and accelerate the powder as it moves down thebarrel. The powder is entrained for a sufficient distance for it to beaccelerated to a high velocity and for virtually all of the powder tobecome molten. A pulse of inert nitrogen gas is used to purge the barrelafter each detonation. The process may be repeated many times persecond. Each detonation results in the deposition of a coating material,a few microns thick on the surface of the matrix bit body. Additionally,although most coating materials are heated to temperatures well beyondtheir melting points, substrate temperatures generally remain very low.Thus, in various embodiments, a reinforcing overlay applied by a d-gunprocess may be applied either prior to or subsequent to brazing of thecutting elements to the bit body.

The high velocity cold spray, such as that described in U.S. Pat. No.6,780,458, which is herein incorporated by reference in its entirety,involves a kinetic spray process that uses supersonic jets of compressedgas to accelerate near-room temperature powder particles at ultra highvelocities. The unmelted particles, traveling at speeds between 500 to1,500 m/sec plastically deform and consolidate on impact with theirsubstrate to create a coating. The basis of the cold spray process isthe gas-dynamic acceleration of particulates to supersonic velocities(500-1500 m/sec), and hence high kinetic energies, so that solid-stateplastic deformation and fusion occur on impact to produce dense coatingswithout the feedstock material being significantly heated.

The spray-and-fuse process is a two-step process in which a powderedcoating material is deposited by using either a combustion gun or plasmaspray gun, and subsequently fused to the matrix body substrate usingeither a heating torch or a furnace, for example, to temperaturesranging from 700-1200° C. depending on the melting point of the overlaymaterial. The coatings are usually made of nickel or cobalt self-fluxingalloys to which hard particles, such as tungsten carbide, may be addedfor increased wear resistance. A reinforcing overlay having the desiredthickness may be formed by building up several layers at a rate of 0.005to 0.030 inches per pass. Deposit thickness is controlled by thetraverse speed of rotation (when done between centers on cylindricalparts), powder flow, and the number of layers applied.

Among other typical thermal spray process that may be used are highvelocity oxy-fuel spraying (HVOF), high velocity air fuel spraying(HVAF), flame spray, plasma spray or other applicable process as knownby one of ordinary skill in the art.

Among the welding techniques that may be used are an oxyacetylenewelding process (OXY), plasma transferred arc (PTA), an atomic hydrogenwelding (ATW), welding via tungsten inert gas (TIG), gas tungsten arcwelding (GTAW) or other applicable processes as known by one of ordinaryskill in the art.

While above embodiments make reference to tungsten carbide particles, nolimitation is intended on the scope of the invention by such adescription. It is specifically within the scope of the presentinvention that other “hard materials” such as metal oxides, metalnitrides, metal borides, other metal carbides, and alloys thereof may beused.

Advantageously, embodiments disclosed herein provides for a fixed cutterdrill bit that may simultaneously achieve the inversely relatedproperties of toughness and wear/erosion resistance. A matrix bit bodythat includes a reinforcing overlay disclosed herein may possess thebenefits of a tough core, providing resistance to cracking, and asuperior wear resistant surface. Furthermore, it is generallynecessitated that conventional matrix body bits are designed bybalancing toughness and wear/erosion resistance; however, the bitsdisclosed herein may allow for a matrix bit body having improvedtransverse strength and toughness with aggressive blade design, withoutthe concern of blade failure by erosion or wear. The combination of thetough core and superior wear/erosion resistant exterior may allow fasterrate of penetration, superior cutting element retention strength anddurability due to the protected cutter surface by preventing erosion ofthe braze alloy and other areas surrounding the cutters, improved bitlife due to minimal erosion of the bit body, and rebuildability of thebit.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A drill bit, comprising: a matrix bit body having a reinforcingoverlay thereon and having at least one blade thereon; at least onecutter pocket disposed on the at least one blade; at least one cutterdisposed in the at least one cutter pocket; and a braze materialdisposed between the at least one cutter and the at least one cutterpocket, wherein the reinforcing overlay comprises carbide particles andat least one binder and has a melting point greater than a melting pointof the braze material.
 2. The drill bit of claim 1, wherein the at leastone binder comprises at least one of nickel, cobalt, iron, and alloysthereof.
 3. The drill bit of claim 1, wherein the reinforcing overlayhas a hardness greater than about 50 HRc.
 4. (canceled)
 5. The drill bitof claim 1, wherein the reinforcing overlay has a thickness ranging fromabout 0.010 to 0.125 inches.
 6. The drill bit of claim 1, wherein thematrix bit body comprises a matrix of tungsten carbide particles and asecond binder.
 7. The drill bit of claim 6, wherein the second bindercomprises at least one of nickel, cobalt, iron, and copper.
 8. The drillbit of claim 6, wherein the second binder comprises about 30 to 40volume percent of the matrix bit body.
 9. The drill bit of claim 1,wherein the reinforcing overlay comprises a plurality of layers. 10.(canceled)
 11. The drill bit of claim 1, wherein the reinforcing overlayhas a melting point greater than 1000° C.
 12. A drill bit, comprising: amatrix bit body having a reinforcing overlay thereon and having at leastone blade thereon; at least one cutter pocket disposed on the at leastone blade; at least one cutter disposed in the at least one cutterpocket; and a braze material disposed between the at least one cutterand the at least one cutter pocket, wherein the reinforcing overlaycomprises carbide particles and at least one binder and has a hardnessgreater than about 50 KRc.
 13. (canceled)
 14. The drill bit of claim 12,wherein the reinforcing overlay has a hardness ranging from about 50 to75 HRc.
 15. The drill bit of claim 12, wherein the matrix bit body has ahardness ranging from about 38 to 45 HRc.
 16. The drill bit of claim 12,wherein the reinforcing overlay has a thickness ranging from about 0.010to 0.125 inches.
 17. The drill bit of claim 12, wherein the matrix bitbody comprises a matrix of tungsten carbide particles and a secondbinder.
 18. The drill bit of claim 17, wherein the second bindercomprises at least one of nickel, cobalt, iron, and copper.
 19. Thedrill bit of claim 17, wherein the second binder comprises about 30 to40 volume percent of the matrix bit body.
 20. A method of forming adrill bit, comprising: forming a matrix bit body having at least oneblade thereon, wherein the at least one blade has at least one cutterpocket disposed thereon; applying a reinforcing overlay to the formedmatrix bit body; and brazing at least one cutter in the at least onecutter pocket with a braze material.
 21. The method of claim 20, whereinforming the matrix bit body comprises infiltrating a mold filled withcarbide particles with a first binder.
 22. The method of claim 20,wherein forming the matrix bit body comprises hot-pressing carbideparticles with a first binder.
 23. The method of claim 20, whereinapplying the reinforcing overlay comprises using at least one of aspray-and-fuse, d-gun, HVOF, and high velocity cold spray.
 24. Themethod of claim 20, wherein the reinforcing overlay comprises carbideparticLes and a second binder selected from at least one of nickel andcobalt.
 25. The method of claim 20, wherein the reinforcing overlay hasa melting point greater than a melting point of the braze material. 26.The method of claim 20, wherein the forming the matrix bit body andapplying the reinforcing overlay occur simultaneously.
 27. The method ofclaim 20, wherein the applying the reinforcing overlay occurs prior tothe brazing the at least one cutter.
 28. The method of claim 20, whereinthe applying the reinforcing overlay occurs after the brazing at leastone cutter.